In late years, a gyro sensor has been increasingly used in various systems and apparatuses, such as a suspension or airbag control system for automobiles, an inertial navigation system for airplanes and a blurring-correcting apparatus for cameras. This type of gyro sensor is operable, when an angular velocity due to an external force acts on a mass body which is being vibrated at a predetermined movement velocity, to measure a resulting Coriolis force so as to determine the angular velocity. Specifically, the Coriolis force is proportional to a vector product of the angular velocity caused by the external force and the movement velocity of the mass body, and thereby a value corresponding to the angular velocity can be derived from the measured Coriolis force and the known movement velocity of the mass body.
For example, as this type of gyro sensor, Japanese Patent Laid-Open Publication No. 2003-194545 discloses a gyro sensor provided with MEMSs and prepared through a semiconductor production process. The gyro sensor disclosed in the Japanese Patent Laid-Open Publication No. 2003-194545 is provided with a mass body to be driven in such a manner as to be vibrated in a Z-direction perpendicular to the surface of a drawing, and designed to measure an angular velocity acting in an X-direction which is one of the directions along the surface of the drawing. More specifically, as shown in FIG. 35, the gyro sensor comprises a rectangular frame-shaped driven mass body (first mass body) 62, a detection mass body (second mass body) 63 disposed on the inward side of the driven mass body 62, four first springs 64 attached, respectively, to the central portions of four edges of the driven mass body 62 and fixed to a support base plate (not shown), and four second springs 65 extending in the X-direction to connect between opposite ends of each of right and left edges of the driven mass body 62 and corresponding upper and lower edges of the detection mass body 63. Each of the upper and lower edges of the driven mass body 62 is provided with a driving electrode 66 to be applied with a drive voltage so as to vibrate the driven mass body 62 and the detection mass body 63 in the Z-direction. Further, each of the right and left edges of detection mass body 63 is provided with a horizontal detection electrode 67 for detecting a Y-directional displacement of the detection mass body 63 in accordance of change in electrostatic capacitance.
Thus, when an X-directional angular velocity acts on the driven mass body 62 under the condition that a drive voltage is being applied to the driving electrode 66 to continuously vibrate the driven mass body 62 and the detection mass body 63 in the Z-direction, the driven mass body 62 is displaced in the X-direction. The detection mass body 63 is connected to the driven mass body 62 through the second springs 65 extending in the X-direction. Thus, in conjunction with the X-directional displacement of the driven mass body 62, the detection mass body 63 is also displaced in the X-direction. Then, the second spring 65 is bent due to a Coriolis force generated in the detection mass body 63, and thereby the detection mass body 63 is displaced in the Y-direction. This Y-directional displacement of the detection mass body 63 can be measured based on an output of the horizontal detection electrode 67. Therefore, the Coriolis force can be calculated using the Z-directional vibration given to the driven mass body 62 and the output of the horizontal detection electrode 67, so as to allow a value corresponding to the angular velocity to be derived.
The Japanese Patent Laid-Open Publication No. 2003-194545 also discloses other arrangements, wherein one arrangement is designed such that the four first springs 64 are attached, respectively, to four corners of the driven mass body 62, and another arrangement is designed such that one end of each of the second springs 65 is fixed to the support base plate instead of the first springs 64, and the driven mass body 62 and the detection mass body 63 are connected to one another through the first springs 64. As the arrangement designed to fix one end of each of the second springs 56 to the support base plate, the Publication discloses one type in which the other end of the second spring 56 is connected to the detection mass body 63, and another type in which the other end of the second spring 56 is connected to the driven mass body 62.
In the gyro sensor disclosed in the Japanese Patent Laid-Open Publication No. 2003-194545, the driven mass body 62 and the detection mass body 63 are constrained from four sides by the first springs 64 and the second springs 65. Further, each of the driven mass body 62 and the detection mass body 63 is made from a semiconductor substrate, and the support base plate to be joined with the first springs 64 or the second springs 65 is typically made using a glass substrate. Thus, a thermal stress will be generated in the first springs 64 or the second springs 65 due to the difference between respective thermal expansion coefficients of the semiconductor substrate and the glass substrate causes, which leads to change in resonance frequency of the gyro sensor. The change in resonance frequency of the gyro sensor inevitably causes variation in detection value. Therefore, the gyro sensor disclosed in the Japanese Patent Laid-Open Publication No. 2003-194545 involves a problem about a relatively large temperature dependence of a detection value.